linux-kernel - Re: [PATCH 1/3] kexec: Do not map the kexec area as decrypted when SEV is active

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Date:   Mon, 25 Mar 2019 17:17:55 +0000
From:   "Singh, Brijesh" <brijesh.singh@....com>
To:     Borislav Petkov <bp@...en8.de>, lijiang <lijiang@...hat.com>
CC:     "Singh, Brijesh" <brijesh.singh@....com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "kexec@...ts.infradead.org" <kexec@...ts.infradead.org>,
        "tglx@...utronix.de" <tglx@...utronix.de>,
        "mingo@...hat.com" <mingo@...hat.com>,
        "x86@...nel.org" <x86@...nel.org>, "hpa@...or.com" <hpa@...or.com>,
        "akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
        "dyoung@...hat.com" <dyoung@...hat.com>,
        "Lendacky, Thomas" <Thomas.Lendacky@....com>,
        "bhe@...hat.com" <bhe@...hat.com>
Subject: Re: [PATCH 1/3] kexec: Do not map the kexec area as decrypted when
 SEV is active

Hi Boris,


On 3/25/19 1:37 AM, Borislav Petkov wrote:
> On Mon, Mar 25, 2019 at 09:58:07AM +0800, lijiang wrote:
>> For the SEV virtual machine, it maps the kexec memroy area as
>> encrypted, so, no need to invoke this function to change anything.
> 
> Look at the code:
> 
> set_memory_decrypted->__set_memory_enc_dec
> 
> It already *does* invoke this function.
> 

By default all the memory regions are mapped encrypted. The
set_memory_{encrypt,decrypt}() is a generic function which can be
called explicitly to clear/set the encryption mask from the existing
memory mapping. The mem_encrypt_active() returns true if either SEV or 
SME is active. So the __set_memory_enc_dec() uses the
memory_encrypt_active() check to ensure that the function is no-op when
SME/SEV are not active.

Currently, the arch_kexec_post_alloc_pages() unconditionally clear the
encryption mask from the kexec area. In case of SEV, we should not clear
the encryption mask.



>>> 	if (!mem_encrypt_active())
>>>
>>> and heads will spin from all the checking of memory encryption aspects.
>>>
>>> So this would need a rework so that there are no multiple confusing
>>> checks.
>>
>> About the three functions, here i copied their comment from the arch/x86/mm/mem_encrypt.c
>> Please refer to it.
> 
> I know that comment - I have asked for it. Now you go and look at the
> code again with your patch applied.
>